This study aimed to expand knowledge regarding chronic disease and readmissions in the elderly The researchers conducted a retrospective analysis of California Office of Statewide Health Planning and Development Patient Discharge Data, 2000-2009, which includes all adults age 18 and older with a non-federal acute care hospital discharge (n= 29,009,966 discharges). We identified 7- and 30-day all cause readmissions (ACR) and potentially preventable readmissions (PPR), and then analyzed relationships between index and readmission hospitalizations for each metric. They found that in the eligible samples, the 30-day ACR and PPR rates were 10.0% and 5.6% respectively. Index admissions for Heart Failure had the most 30-day ACRs and highest readmission rate (103,591, 19.8%) among medical APR-DRGs, while Other Vascular procedures had the highest rate (14,635, 14.6%) among surgical APR-DRGs. Overall, relatedness of readmissions did not differ for 7- vs. 30-day ACRs. The PPR algorithm captured fewer unrelated readmissions than did the ACR for surgical but not medical APR-DRGs. Unrelated readmission captured by PPR included both acute and chronic conditions, in particular ambulatory care sensitive conditions. This study demonstrates that the concept of relatedness is similar to, but not identical to “potentially preventable” as determined by the PPR metric. Both the ACR and PPR provide a unique perspective on readmissions and can be useful across applications. The reasons for readmission captured by both metrics can provide guidance for potentially impactful interventions. Three manuscripts related to the project have been published by Health Services Research, American Journal of Medical Quality, and the International Journal for Quality in Health Care, and a fourth manuscript is under review.